Add `CheckMetadataHash` signed extension #799

Job	Run time
build	32s
build-try-runtime-and-benchmarks	32s
Rust check +nightly fmt --all -- --check (x86_64-unknown-linux-gnu)	26s
Cancel Previous Runs	2s
Build Runtimes (encointer-node-notee)	20s
Rust check clippy -p encointer-client-notee (x86_64-unknown-linux-gnu)	20s
unit-tests	31s
cargo-toml-fmt	17s
${{ matrix.test }}	1s
Draft Release	1s
Publish Runtimes	1s
	3m 3s

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